Conventional key input devices are equipped with an illuminating unit for lighting a keyboard for use in a dark place such as at night. One example of these conventional key input devices is disclosed in the Japanese Patent Unexamined Publication No. H2005-32703. This illuminated input device includes a base member, PC-board, illuminant, light guide, reflection member, pressure-sensing member, light-reducing member, and input member. The illuminated input device is configured in such a way that a light of the illuminant disposed on the PC-board is reflected on a dot pattern of the light guide, and illuminates the input keys.
In the above conventional structure, however, all members including the PC-board, illuminant, light guide, reflection member, and pressure-sensing member configured inside are sensitive to water. In order to provide a waterproof structure as a countermeasure, water needs to be completely blocked between an upper part consisting of the rubber input member and a lower part consisting of the base member so as to protect internal components from water. In addition, if the input member is made of resin, a waterproof structure cannot be provided because the input member is not integrally formed together.